The present invention relates to contact films, or more particularly to contact films which do not contain silver halide compounds as part of their light sensitive coating.
Conventionally, in the preparation of light sensitive lithographic printing plates, an image is imparted to such plate via contact exposure or projection through a photographic mask. Such a mask typically comprises a transparent support and a photosensitive composition on the transparent support. This photosensitive composition is typically exposed to an original image sought to be reproduced, and developed. The vast majority of such photomasks employ silver halide gelatin compositions on the support as the imaging agent. With the recent dramatic increases in the cost of silver and its reclamation, users of such films have desired a film having the benefits of silver halide films yet which do not contain silver. Although this has been a goal of the art and many substitutes have been proposed, these have not been satisfactory to those skilled in the art of printing plate manufacture and use. These proposals are based upon diazo-coupler or photopolymer systems as the means of creating a UV activated, developer differentiated imaging method. These systems have severe shortcomings in the areas of proper light transmission density, exposure speed, speed of development, developer properties and opacity to UV radiation after exposure and development. Such films therefore find their usefulness primarily as proofing or duplicating films and not as high density films which may be used to expose printing plates as they are aesthetically unsatisfactory due to their color and high transmission of visible light.
The present invention overcomes these problems to provide a photographic element which has sufficient light sensitivity to be exposable within a commercially feasible time; is developable with a fluid developer so as to quickly and completely remove the non-image areas; and possesses sufficient opacity in the non-removed areas so it will be useful to block sufficient ultraviolet radiation when used as a mask to further expose lithographic printing plates or other photographic elements.